pg_pconnect()

(PHP 4, PHP 5, PHP 7)

打开一个持久的 PostgreSQL 连接

说明

pg_pconnect(string $connection_string[,int $connect_type]): resource

pg_pconnect()打开一个到 PostgreSQL 数据库的持久连接。返回其它 PostgreSQL 函数所需要的连接资源号。

If a second call is made to pg_pconnect() with the same$connection_stringas an existing connection, the existing connection will be returned unless you pass PGSQL_CONNECT_FORCE_NEW as$connect_type.

要打开持久连接功能，php.ini中的pgsql.allow_persistent参数必须为"On"（也是默认值）。最大持久连接数目由php.ini中的pgsql.max_persistent参数定义（默认为-1 表示没有限制）。所有连接的数目可由php.ini中的pgsql.max_links参数设置。

pg_close()不能关闭由pg_pconnect()打开的持久连接。

参数

$connection_string

The$connection_stringcan be empty to use all default parameters, or it can contain one or more parameter settings separated by whitespace. Each parameter setting is in the formkeyword = value. Spaces around the equal sign are optional. To write an empty value or a value containing spaces, surround it with single quotes, e.g.,keyword ='a value'. Single quotes and backslashes within the value must be escaped with a backslash, i.e.,' and .

The currently recognized parameter keywords are:$host,$hostaddr,$port,$dbname,$user,$password,$connect_timeout,$options,$tty(ignored),$sslmode,$requiressl(deprecated in favor of$sslmode), and$service. Which of these arguments exist depends on your PostgreSQL version.

$connect_type

If PGSQL_CONNECT_FORCE_NEW is passed, then a new connection is created, even if the$connection_stringis identical to an existing connection.

返回值

PostgreSQL connection resource on success,FALSE on failure.

范例

Example #1 Using pg_pconnect()

<?php
$dbconn = pg_pconnect("dbname=mary");
//connect to a database named "mary"
$dbconn2 = pg_pconnect("host=localhost port=5432 dbname=mary");
// connect to a database named "mary" on "localhost" at port "5432"
$dbconn3 = pg_pconnect("host=sheep port=5432 dbname=mary user=lamb password=foo");
//connect to a database named "mary" on the host "sheep" with a username and password
$conn_string = "host=sheep port=5432 dbname=test user=lamb password=bar";
$dbconn4 = pg_pconnect($conn_string);
//connect to a database named "test" on the host "sheep" with a username and password
?>

参见

pg_connect()打开一个 PostgreSQL 连接
持久数据库连接

You should not use pg_pconnect - it's broken. It will work but it doesn't really pool, and it's behaviour is unpredictable. It will only make you rise the max_connections parameter in postgresql.conf file until you run out of resources (which will slow your database down).
If you have many concurrent connections to your database, you should use the PostgreSQL connection pooler PgBouncer (developed by the Skype-team). When using pgbouncer, make sure you use pg_connect and NOT pg_pconnect. Also, make sure you close your connections with pg_close.
* PGBouncer homepage:
http://developer.skype.com/SkypeGarage/DbProjects/PgBouncer
* PostgreSQL pooling article by Last.fm:
http://www.last.fm/user/Russ/journal/2008/02/21
/zd_postgres_connection_pools:_pgpool_vs._pgbouncer

As of Aug 2007, some suggestions from the postgresql forums
on pg_pconnect(), faster postgres connections, and connection pooling:
Summary: 
http://archives.postgresql.org/pgsql-general/2007-08/msg01406.php
Good details: http://archives.postgresql.org/pgsql-general/2007-08/msg00660.php
Also: http://archives.postgresql.org/pgsql-general/2007-08/msg01489.php

A contribution to the transaction issue raised by "garrett at bgb dot cc".
In a German book about PostgreSQL in connection with PHP (Cornelia Boenigk, PostgreSQL - Grundlagen, Praxis, Anwendungsentwicklung mit PHP) one can read in chapter 19.3 about persistent connections:
If the page processing aborts and the transaction is not finished yet, the next script using the same persistent connection will be considered as the continuation of the transaction. In particular a lock of a table will persist. The explanation is as follows: After the abort of the script no COMMIT or ROLLBACK was sent to the db server.
The author describes a hint to avoid the scenario above:
You can create a function for resolving transactions and locks erroneously not closed. For invoking the function after execution of a script it has to be registered with the function register_shutdown_function():
 http://de2.php.net/manual/en/function.register-shutdown-function.php

For resetting an apache web server and in same time the persistent connections you may use :
./apachectl graceful

How to reset persistent connections:
killall -USR1 httpd

If a transaction is in progress when page processing ends, is it aborted before the connection placed bak in the pool? Or is the connection added "as is"?
It would seem that the correct thing to do is to always 'ABORT' before adding to the pool. 
As a note, this would be a good time to check and see if the connection is still open before readding it. Thus allowing closed connections to be cleaned up over time, instead of hanging around for ever as they do now.

Instead of reducing MaxClients in apache you may try to
reduce pgsql.max_links in php to at least the number of
postmasters. It should work and leave
you with more available httpds for static html pages.

Be careful when using Apache/PHP dynamic module/PostgreSQL :
in httpd.conf (Apache conf) default MaxClients is 150, whereas default PG's max_connections is 32 which is much fewer than 150. You have to set max_connections to at least MaxClients (and pg's shared_buffers to 2*max_connections at least) to avoid PG's errors with pg_pconnect like : "Sorry, too many clients already connected"

To setup a high availability server with apache as a static module and postgreSQL, change httpd.conf and set MaxClients to less than max postgreSQL simultaneous connections (like 32 or 64).
This way pg_pconnect will allways return a valid handle under heavy traffic or under a request flow attack without wasting resources and without connection problems.

<?php
//
// Using pg_pconnect in a class.
//
// Why this? Because the manual says:
//
//  If a second call is made to pg_pconnect() with the same
//  connection_string as an existing connection, the existing 
//  connection will be returned unless you pass 
//  PGSQL_CONNECT_FORCE_NEW as connect_type.
//
// This is not always true.
//
/**
 * MyClassA creates a postgresql connection using pg_pconnect 
 * and stores the resulting resource id to $this->conn 
 */
class MyClassA
{
  function __construct($connection_string)
  {
    $this->conn = 
      pg_pconnect($connection_string) 
        or die('Wrong CONN_STRING');
  }
}
//
// Showing current php.ini settings to be sure
// that persistent connections s are allowed. 
// -1 means 'unlimited'
//
echo '<br>pgsql.allow_persistent: ' . ini_get('pgsql.allow_persistent');
echo '<br>pgsql.max_persistent: ' . ini_get('pgsql.max_persistent');
echo '<br>pgsql.max_links: ' . ini_get('pgsql.max_links');
echo '<br><br>';
// setting one custom connection string for all objects
// (modify $connection_string to fit your needs)
$connection_string =
  'host=localhost port=5432' .
  ' dbname=test user=test password=test';
// 
// Creating 10 MyClassA objects using the same $connection_string
//
$objArr = Array();
for ($i = 0; $i < 10; $i++) 
{
  $objArr[] = new MyClassA($connection_string);
}
//
// Human readable result:
//
foreach($objArr as $id => $object)
{
  printf(
    '%s: Object %s: using db %s<br>',
    get_class($object), $id, $object->conn
  );
}
/* ------------------------------------------------------------- */
// The result
// pgsql.allow_persistent: 1
// pgsql.max_persistent: -1
// pgsql.max_links: -1
// 
// MyClassA: Object 0: using db Resource id #2
// MyClassA: Object 1: using db Resource id #3
// MyClassA: Object 2: using db Resource id #4
// MyClassA: Object 3: using db Resource id #5
// MyClassA: Object 4: using db Resource id #6
// MyClassA: Object 5: using db Resource id #7
// MyClassA: Object 6: using db Resource id #8
// MyClassA: Object 7: using db Resource id #9
// MyClassA: Object 8: using db Resource id #10
// MyClassA: Object 9: using db Resource id #11
// 
/* ------------------------------------------------------------- */
//
// Each MyClassA object will use its _own_ database Resource id
//
?>